The present invention relates to systems widely used in large spaces, such as shops or work rooms, for providing audio information and/or visual information to people moving in the rooms in question. In particular, the invention relates to a sound reproduction system comprising a plurality of separate loudspeaker units via which information is transmitted, as well as to a method for implementing a system of this kind.
The sound reproduction system in accordance with the invention is thus intended for use in large spaces, particularly in shopping centres or large shops where there is a need to transmit current, situation-specific or individual information to customers or other people moving in the room in question. A large space refers herein to the space in which the sound reproduction system is situated. This space is typically larger than a normal room (or e.g. a studio), usually a public space which may be either a roofed or an open space.
As to the terms "sound-reproduction system" and "loudspeaker unit" used in this description, it must be stated that they are used since in almost all the embodiments of the system, at least audio information is transmitted. It must be understood, however, that said terms also cover such an embodiment in which a "loudspeaker unit" only comprises a display unit for transmitting textual information (this relates to solutions in accordance with the attached claims 1 and 12).
The aim of a sound reproduction system used in a large space, such as a shopping centre, is to create a sound background suitable for the function of the space in question. Sound reproduction is usually carried out by means of several loudspeakers, to which common audio information (typically background music) is supplied from a common sound source via fixed wiring. Acoustics management in a large space of this kind is often problematic, however, since the circumstances may differ from each other a great deal in different parts of the space. Acoustics management is further complicated by the fact that some of these differences are constant in proportion to time, and others, in turn, vary in proportion to time.
Sound pressure levels used in spaces of this kind are usually low, and the listening is usually such that the sounds are heard in the background. The sound pressure level varies in sequences e.g. depending on the number of visitors. The clarity of the audio message depends on the ratio of the background noise and the useful sound, and only a sufficient excess over the background noise enables understanding the message. On the other hand, too strong a sound background is often perceived as disturbing.
As mentioned above, this kind of a sound reproduction system of a large room or another space is typically implemented by means of a plurality of loudspeakers which are connected to the sound source via a fixed wiring. Prior art methods and systems of this kind do not, however, enable effective management of a rapidly varying acoustic environment of a large room in order that the audio message be as clear as possible in different and varying conditions.
Another important drawback of these prior art methods is their inability to concentrate different types of acoustic information into a smaller part of the whole space simultaneously, that is, instructive information or shop advertising for certain (different) groups of customers moving in different parts of the space covered by the system.
In typical prior art solutions, cabling costs are high, and possibilities of making flexible changes are weak. In addition, it is difficult to implement mobile sound reproduction systems.
Prior art sound reproduction systems for large spaces do not enable a flexible sound reproduction system either. In a flexible sound reproduction system measurements are carried out in a room (small space), and on the basis of these measurements the operation of the sound reproduction system is adjusted.
In some of the prior art systems more flexibility has been aimed at by combining each loudspeaker unit (having a unique address) to the data and audio bus of the system, whereby the desired loudspeaker units can be turned off via a common central processing unit and a desired audio message can be sent only via specific loudspeakers. This type of sound reproduction system, or a public address system is disclosed in British Patent No. 2,123,193. In the loudspeaker unit of this system it is also possible to test whether an individual loudspeaker is operating, and to send the information on the test to the central processing unit. Although some more flexibility has been gained by means of the system, the major drawbacks described above still exist, particularly the inability to send information specific to the state of an individual loudspeaker unit to each loudspeaker unit.